gistfile1.m

[_photo_library
    assetForURL: url
    resultBlock:^(ALAsset *asset)
    {
	ALAssetRepresentation * rep  = [asset defaultRepresentation];
	NSDictionary          * meta = [rep   metadata];
			
	if( meta[ @"AdjustmentXMP" ] ) {
	    // Image is filtered, add to list
	}
    }
];